78 PHOLADID^. 



elevated concentric approximate lines, which are more 

 closely set as they recede from the apex of the valves ; the 

 slightly raised, narrow, ray-like strip, which skirts the 

 lower half of the anterior side, passing upwards to the 

 beaks, is likewise crowded with very delicate elevated 

 oblique lines, decussated (though scarcely so closely as in 

 Norvagicd) with microscopic striulae. Behind these, an- 

 other, narrow ray-like space appears, extending from the 

 beaks to the most projecting part of the ventral margin, 

 and usually lying about the middle of the valves. This 

 area is rather distantly traversed, in a concentric direction, 

 by arched and imbricated elevated strise, and obsoletely 

 and radiatingly subdivided by the hinder portion being dis- 

 tinctly concave, and the front rendered slightly duller in 

 surface, from the intervals of the strise being filled up in 

 the adult with microscopic striulee. The remaining or 

 posterior surface, which is smooth and glossy, but some- 

 times traversed by remote and obsolete lines of growth, is 

 again convex, the gradual cessation of Avhich convexity 

 marks the commencement of the auricle, which is not 

 otherwise externally defined, and is only so internally by 

 its immediate reflexion, and the previous thickening of 

 the body or middle part of the valves at that point ; there 

 being neither carination present, nor the slightest appear- 

 ance of an overlapping margin. The extraordinary deve- 

 lopment of the auricle is evidently the typical characteristic 

 of the species. Decidedly reflected at its outer extremity, 

 its surface, in consequence, is retuse or concave ; its margin, 

 arching out laterally in one uninterrupted sweep from its 

 base to its summit, towers a little above the beaks, and 

 being met, not far from them, by the short, ascending, and 

 deeply incurved dorsal edge, seems retusely subtruncated 

 near its highest elevation. It thus projects both laterally 



